Antenna



United States Patent O ANTENNA William Sichak, Lyndhurst, N. J., assiguor to International Telephone and Telegraph Corporation, a corporation of Maryland Application April 18, 1949, Serial No. 88,110

12 Claims. (Cl. 343-756) This invention relates to electromagnetic wave energy reflectors and more particularly to such reflectors having selective directional characteristics.

A principal object of the invention is to provide a reflector for electromagnetic wave energy which is selectively responsive to incident elds of different polarizations.

Another object is to provide a reflector for electromagnetic wave energy, which can be used to receive and selectively segregate wave energies arriving at the reflector from different directions.

A feature of the invention relates to a reflector of the type having a plurality of spaced strips for reflecting electromagnetic wave energy, whereby incident energy can be selectively reflected into two segregated paths, and the amount of the reflected energy in the two paths can be controlled by variation of the angular relation between the polarization plane of the incident wave energy and the plane of said reflector strips.

Another feature relates to a selective reflector for electromagnetic wave energy comprising a series of conductive strips mounted in front of a common conductive reflecting plate with the front edges of the strips having a predetermined angular relation with respect to the plane of said reflector plate.

Another feature relates to a selective reflector for electromagnetic Wave energy, comprising a reflector plate having attached thereto a plurality of sets of spaced parallel metal strips whose planes are perpendicular to the reflector plate, the strips having their front edges inclined to the reflector plate and being of progressively different lengths considered from the center to the lateral edges of the plate.

Another feature relates to a reflector for electromagnetic wave energy whereby the angle between incident and reflected fields can be adjusted by orienting the reflector with respect to the polarization of the incident field.

Another feature relates to the combination of a plurality of radiation sources of different polarization cooperating with a single reflector which has the property of reflecting the radiation in segregated paths.

A further feature relates to a parabolic reflector consisting of a backing plate having attached to its reflecting surface a series of conductive linear elements in the form of wires or strips, the reflecting edges of said wires or strips being arranged to form another parabola or quasiparabola whereby two radiation sources or responsive devices can cooperate simultaneously with the reflector without undesirable cross-talk.

The above-mentioned and other features and objects of this invention and the manner of attaining them will become more apparent and the invention itself will be best understood, by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein,

Fig. 1 is a perspective view of a reflector according to the invention.

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Fig. 2 is a vertical side view of Fig. l.

Fig. 3 is a diagrammatic front view, explanatory of the operation of the reflector.

Fig. 4 is another diagrammatic front view of the reflector also explanatory of its operation.

Fig. 5 is a diagrammatic side view of a modified form of reflector.

Fig. 6 is a front view of the reflector of Fig. 5.

Fig. 7 is a diagrammatic view of a modification of the invention.

Fig. 8 is a front view of the reflector of Fig. 7.

Fig. 9 is a diagrammatic view of a further modification of the invention.

Fig. 10 is a front view of the reflector of Fig. 9.

Referring to Figs. l and 2, the preferred form of the reflector according to the invention comprises a flat plate 1 of metal or other conductive material which acts in the nature of a plane reflector for incident electromagnetic wave energy. Suitably fastened to one face of plate 1 are a series of parallel metal strips, an arbitrary number of which are shown in the drawing. It will be understood, of course, that a greater or lesser number of such strips can be employed. Preferably, although not necessarily, the strips 2 are spaced apart a distance D somewhat less than one-half the wavelength k of the incident electromagnetic wave energy which is represented by the arrow 3. Preferably, the reflector is supported and oriented so that the incident fields arrive in a direction parallel to the planes of the strips 2, otherwise the reflector plate 1 will be effectively shielded to some extent by the said Strips. In effect therefore, each pair of adjacent strips forms a rectangular wave guide terminating in the reflector plate 1, where the depth W of the strips, considered in a plane perpendicular to plate 1, depends upon the spacing D between the strips. In accordance with the wellknownftheory of rectangular wave guides, the larger the spacing D, the greater must be the depth W, in order to maintain the same wave attenuation for the parallel electric components of the incident field.

In accordance with one feature of the invention, the front edges of the strips 2, as shown in Fig. 2, are inclined at a predetermined angle A with respect to plate 1, since it has been found that this angle determines the angle between the reflected beams produced by incident beams of different polarizations. Thus if the incident field of electromagnetic wave energy is polarized in a plane normal to the planes of strips Z, the reflected field will be mainly derived from reflections from the back plate 1 because, for such polarization, the strips apparently act as a stack of wave guides with large width and small height for the electric field lines propagated therebetween. This condition is represented in Fig. 2, wherein the dots 4 represent the direction of the electric field lines extending perpendicular to the plane of the drawing, and also in Fig. 3 by the arrows 5. On the other hand, when the polarization of the incident field 3 is parallel to strips 2, the reflection will be mainly from the inclined front edges of the strips because yfor this polarizatiom'adjacent strips apparently act as wave guides with small width and large height, so that in effect each wave guide is beyond cut-off. This relation is represented by the dotted arrows 6 in Figs. 2 and 4.

Preferably, although not necessarily, the strips 2 are of such respectively different lengths that their peripheral boundary line is substantially elliptical, as is the backing plate 1. In one reflector that was found to have the desired characteristics, the reflector was elliptical in shape having a minor axis of 18 inches, a major axis of 25 inches, the strips 2 being spaced apart a distance of one inch which is equal to 0.4) where t. is the wavelength of the incident radiation 3. The angle A between the plate 1 and the front edges of the strips 2 was 21,/2, and the minimum depth W of the strips at their shallow end was one inch. To determine the selective directional characteristics of the reflector, an electromagnetic transmitting horn 7 can be mounted approximately nine feet away from the reflector, and radiating waves with a polarization perpendicular to the plane of the strips 2, as represented by the beam 8. An electromagnetic receiv` ing horn 9 can be mounted approximately eleven feet away from the reflector. With this orientation of the polarization of the incident waves, as represented by the dots 4 (Fig. 2), the angle between the incident beam 8 and the reflected beam 10 was approximately 90. The polarization from the transmitting horn 7 was then changed to a polarization parallel to the strips 2, as represented by the arrow 6 and the beam 11. The reflected beam for this condition is indicated by the numeral 12. lt was found that the angle p between the two reflected beams 10 and 12 was approximately 5 It will be seen from the foregoing that the selective reflecting properties of this new reflector enable it to be used for a number of purposes. Thus it can be used to receive and segregate two radiations arriving from two different directions, or it can be used to transmit in two different directions from two separate transmitters. Likewise, it can be used to segregate two different fields arriving in the same direction with different polarizations. Furthermore, it has been found that the amount of power radiated in each of the two different directions, whether for transmission or reception, can be controlled by varying the relative angular relation a between the plane of the strips 2 and the plane of polarization of the incident wave energy. This relative orientation can of course be effected either by changing the position of the reflector with respect to the polarization plane of the incident waves, or by changing the polarization plane of the waves with respect to the reflector. When the polarization of the incident energy is in a plane parallel to the strips 2, all the reflected power goes in one particular direction with a certain plane of polarization. When the polarization of the incident energy is in a plane' normal to the plane of the strips 2, all the reflected power goes in a different direction and with the conjugate polarization'. For any intermediate angle a between the plane of the incident polarization and the plane of strips 2, the ratio of the reflected powers in the two different directions is cot2 a.

It is of interest to note the case where the strips 2 instead of having their front edges inclined to plate 1, are parallel to that plate. Such an arrangement is illustrated in Fig. 5 and 6, wherein 0 is the angle of incidence between the incident waves and the normal to the strip edges, and a is the angle between the polarization plane of the incident waves and the plane of strips 2. For purposes of explanation, it will be assumed that the "y dimension is along the length of strips 2, and the x dimension is normal to the strips. Then the reflected field is given by jzKW cos 0 where iy=a unit vector in the y direction;

i==a unit vector in the x direction;

W=the depth of the strips.

For this condition, only one beam is reflected, no matter what the polarization angle of the incident field. If the path difference equals a half wavelength M2, the phase ofthe xcomponent is shifted by 180. This occurswhen Wequals'X/ico's 0. Thus when the incident polarization is at`v an angle a (Fig. 6), the reflected field lwill be polarized 90 with respect to the incident field. If, on the other hand, the path difference is other than one-half wavelength, the reflected field will be elliptically polarized. If the angle a is 45 and the path difference is onequarter wavelength (M4), that is, when W equals M 8 cos 0, the reflected field is circularly polarized.

The invention is not limited to the spacing of the strips 2 by a distance less than one-half wavelength. Thus the spacing may be more than M2, with the result that both components propagate between adjacent strips as wave guides. However with such a construction the reflected field can be produced only with circular or elliptical polarization. It has the additional disadvantage when used to produce circular polarization of being more frequency sensitive than where the strip spacing is less than one-half lambda, that is beyond cut-off, because of thc variation of the guide wavelength with frequency.

While in the foregoing, the reflector 1 and the strips 2 may have an elliptical configuration, it will be understood that any other configuration may be employed. Furthermore while the plate 1 is shown as a flat or plane reflector, it will be understood that it may be of parabolic or any other suitable shape. Furthermore the strips 2 instead of being formed of flat metal stock, can be formed of wire mesh or a series of spaced longitudinal wires.

Referring to the modification of Figs. 7 and 8, there are shown two radiation sources 13, 14, which produce fields polarized at 90 with respect to each other. The source 13 may comprise, for example, a radiating dipole 15 and an associated reflector 16. Likewise, the source 14 may comprise a radiating dipole 17 and a reflector 18. Associated with these sources is a selective reflector 19 comprising a backing reflector 20 which is approximately parabolic in shape. Attached to the face 0f plate 20 are a series of parallel metal strips 21 spaced apart a distance D less thanv V2A. These strips, like the strips 2 of Figs. 1 to 4, are of tapered width W for reasons pointed out above. Preferably, the plates 21 are so shaped that the locus of their front edges 22 defines a parabola which has its focus at the source 13, it being understood that the parabolic plate reflector 20 has its focus at the source 14. Assuming that the field from source 13 is polarized in a plane parallel to the plane of the strips 21, the reflected beam is indicated by the arrow 23. Assuming that the field from source 14 is polarized perpendicular to the plane of the strips 21, the reflected beam is indicated by the arrow 24. As a result of the parabolic nature of the reflector 19 as a whole and the relative orientations of the polarizations from the sources 13 and 14, the reflected beams 23 and 24 will be effectively segregated. Since the locus of the front edges of the strips 21 is a parabola, and since the field from the two sources is forced to travel between the strips 21, the plate 20 is not a true parabola. However the equation of its surface is as follows:

where F1=the focal length of the parabola defined by the front edges of the strips 21;

Fz=the focal length of the parabolic surface 20;

X1Y1Z1=the coordinates of the parabola defined by the front edges of the strips 21;

X2Y2Z2=the coordinates of the parabolic surface 20.

One of the advantages of the arrangement of Figs. 7 and 8, is that the reflector surface 20 and the reflector surface formed by the front edges 22 of the strips 21 can be of widely different diameters, thus enabling the same reflected beam widths to be obtained and the same gain to be obtained even though the frequency of source 13 substantially differs from the frequency of source 14.

In certain casesfthelstrips 21 ofFigs. 7 and 8 can bereplaced by'a series of wires or thin metal tubes 25, as

shown in the embodiment of Figs. 9 and 10, these wires or tubes being spaced apart a distance less than 1/2 where )t is the wavelength of the incident radiation. The remaining elements of Fig. 9 may be the same as those of Fig. 7, and the corresponding parts of the two figures are designated alike. In the embodiment of Fig. 9, the wires or tubes 25 correspond to the front edges 22 of the strips 21 (Fig. 7) and preferably, they are inclined to the plate to correspond with the inclination of the said front edges 22 with respect to plate 20.

It will be understood that in the embodiment of Figs. 9 and l0, the wires or tubes 25 are supported by insulation material in the desired spaced relation to each other and to the plate 20 by an insulation material having a suitable dielectric constant, for example dielectric sold under the trade-name Polyfoam having a dielectric constant of -l.1. Preferably the two sources 13 and 14 in Figs. 7 and 9 are fed respectively through the intermediary of a double or telescoped coaxial line. In such a double line, the inner coaxial line has its outer conductor located within the inner conductor of the outer coaxial line.

While in the foregoing embodiments the backing reflector member 1 is in the form of a continuous plate, it will be understood that it can take the form of a wire mesh or the like.

While I have described above the principles of my invention in connection with specific apparatus and dimensions, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of my invention.

What is claimed is:

l. A reflecting arrangement for reflecting differently the components of electro-magnetic waves having different polarization comprising, a backing reflector having a substantially continuous surface, and a plurality of elongated, straight conductor strips positioned edgewise in front of said reflector and spaced apart from each other a distance not greater than substantially a half wave length at the operating frequencies of said electro-magnetic waves to reflect the wave components thereof polarized in a plane normalto the planes of said strips, said conductor strips having their front edges disposed to form together a group of narrow reflecting strips to reflect the wave components polarized in `a plane parallel to lthe planes of said strips.

2. A reflecting arrangement according to claim l, in which said backing plate is a substantially parabolic reflector.

3. A reflecting arrangement yaccording to claim 1, in which said backing plate is a substantially parabolic reflector and the front edges of said strips form a substantially parabolic contour of different focal length from that of the backing plate.

4. A reflecting arrangement for electromagnetic waves of predetermined polarization comprising, a backing rellector having a substantially continuous plane surface, and a plurality of elongated, straight conductor strips, positioned edgewise in front of said reflector and spaced apart from each other a distance not greater than substantially a half-Wave length of the operating frequencies of said electromagnetic waves, said conductor strips having their front edges substantially straight in coplanar relation and inclined at an angle to the plane of said backing reflector.

5. A device for reflecting differently the components of electromagnetic waves having different polarization, comprising a reflector having a -given reflecting surface and a plurality of parallel conductor strips disposed edge wise across the front of said surface dividing said surface into a plurality of narrow parallel areas each of a width not greater than a half-wave length of said electromagnetic waves to reflect the wave component thereof polarized in a plane normal to the longitudinal axes of said areas, and said strips having their front edges dis posed in substantially coplanar relation to reflect the wave component polarized in -a plane parallel to the planes of said strips.

6. A device according to claim 5, wherein said given surface of said reflector is a plane surface and the plane of the front edges of said strips is inclined to the plane of said plane surface.

7. A device according to claim 5, wherein said given surface of said reflector is a plane surface and the plane of the front edges of said strips is parallel to said plane surface.

8. In combination, a plurality of sources of electromagnetic waves of different polarization, a reflector for segregating the waves from said sources `and comprising a plane reflecting plate having attached thereto in edgewise relation a series of spaced metal strips forming a series of effective wave guides for the incident waves.

9. The combination according to claim 8, in which the reflector is oriented wi-th respect to the Waves from said two sources so that the planes of polarization of the waves from the two sources are at different angles with respect -to the length of said strips.

l0. The combination according to claim 8, in which said reflector is oriented with respect to said two sources so that the plane of polarization of the waves from one source is parallel to the leng-th of said strips and the plane of polarization of the waves from the other source is normal to the plane of said strips.

11. In combination, a first radiation antenna, a second radiation antenna, a first substantially parabolic reflector at whose focus the first antenna is located, a second substantially parabolic reflector of shorter focal length than the first reflector and at whose focus the second radiation antenna is located said second reflector comprising a series of spaced parallel metal strips mounted in front of the first reflector, said first antenna being polarized in a different plane from the second antenna said strips being attached to the reflecting surface of the parabolic reflector, the length of said strips extending parallel to the plane of said polarisation of one of said antennas and normal to the plane of polarisation of the other of said antennas.

12. The combination according to claim 11, in which said strips have a graduated depth from each end toward the center thereof.

References Cited in the file of this patent UNITED STATES PATENTS 2,423,648 Hansell July 8, 1947 2,442,951 Iams June 8, 1948 2,464,269 Smith Mar. l5, 1949 FOREIGN PATENTS 582,007 Germany Aug. 7, 1933 668,231 Germany Nov. 28, 1938 

